In computer programming, heisenbug is a classification of an unusual software bug that disappears or alters its behavior when an attempt to isolate it is made. Due to the unpredictable nature of a heisenbug, when trying to recreate the bug or using a debugger, the error may change or even vanish on a retry. The name heisenbug is derived from Heisenberg's Uncertainty Principle which states, "it is fundamentally impossible to predict the position and momentum of a particle at the same time". Contrast with bohrbug.